The present invention is directed to processes for protecting nylon fibers from staining due to colorants such as iodine found in betadine solution, and turmeric found in mustard products while also protecting nylon fiber dyes from fading due to reactive chemical agents such as sodium hypochlorite found in household bleach and bleach cleaners and benzoyl peroxide found in acne care products.
In 1985 the carpet industry began using anionic (negative charged) polymers on acid dyeable nylon fibers to impart stain resistance (stainblocking) to carpets and rugs to protect them from colorant type stains. These stains are caused by dyes in food and drink products that come into contact with nylon fibers. These colorants have the ability to permanently dye the nylon fibers with the severity of the stain being dependent on the type and polymer structure of the fibers. Because acid dyeable nylon fibers are cationic (positive) charged fibers, they tend to stain easily when in contact with anionic (negative charged) colorants such as those in Kool Aid, wine and coffee. Cationic dyeable nylon fibers, however, are anionic (negative) charged fibers and have natural resistance to anionic colorant stains. Although cationic dyeable and stainblocked acid dyeable nylon fibers have negative charges, they both contain similar polymer structures (morphologies).
As a result of the natural stain resistance of cationic dyeable nylon type fibers, there has been an increase in their use over the years, particularly in commercial carpets used for schools, offices, healthcare facilities and in the food service industry. The method for coloration of the cationic dyeable nylon has mostly involved the use of solution dyed nylon fibers. These are dyed nylon fibers where the color (shade) is introduced as a pigment in the manufacturing process of the fibers. The advantage is that the dye pigments in the solution dyed fibers are resistant to fading from chemical agents; whereas, dyestuffs in acid dyed nylon fibers will fade.
A carpet mill dye process method to impart coloration to cationic dyeable nylon fibers (CD-nylon) is disclosed in U.S. Pat. No. 5,058,667. Although the dyes are not resistant to chemical agents by this method, color combinations far above that of solution dyed nylon can be achieved. Regardless of method of coloration, carpet products from both methods are stain resistant to anionic colorant type stain. Similar stain resistance (stainblocking) properties can be achieved using acid dyeable type nylons treated with sulfonated aromatic aldehyde condensation polymers (SAC) and methacrylate type anionic polymers to impart an anionic charge on the fibers similar to that of the cationic dyeable nylon type fibers. These polymers are disclosed in a number of patents such as in U.S. Pat. Nos. 4,822,373, 4,875;901, and 4,937,123. But whether the nylon fibers are naturally or chemically stain resistant, they are not protected against stains from iodine and turmeric (mustard); nor are the dyes on dyed nylon fibers protected against fading from reactive chemical agents contained in bleach and acne care products.
When nylon fibers have a negative charge, either naturally or from stainblocker treatments, there is a charge/charge repulsion between the colorant and the fiber surface. Therefore, an ionic charge repulsion mechanism prevents negatively charged colorants from diffusing to available free amine end groups (dye sites) that are contained in the nylon fibers. As a consequence, a colorant containing product that is spilled on a carpet can be removed by rinsing or extracting with water without leaving a stain. The mechanism by which dyestuffs on dyed nylon are faded by reactive chemical agents is somewhat more complex. Chemicals such as sodium hypochlorite in bleach, and benzoyl peroxide in acne care products, form highly reactive chemical species such as chlorine and benzoyl radical. These species react with organic molecules that surround them, especially those that contain highly unsaturated chemical bonds. Dyestuffs are organic molecules that contain highly conjugated unsaturated molecular arrays. The structure of these arrays account for what is observed as color. The reaction of dyes on nylon fibers with the reactive species in chemical agents destroys the chemical bonds which give dyes color. This decolorizing effect can visually appear as a shade loss, a bleaching effect, or sometimes as a different looking stain. Reactive chemical agents permanently damage dyes on carpet in those areas for which they are in contact.
Although cationic dyeable nylon and stainblocked acid dyeable nylon prevent staining from most colorant stains, they do not prevent stains from iodine in betadine solution or turmeric stains in mustard products. The reason is that colorants contained in betadine and mustard are neutrally charged and are unaffected by a charge/charge repulsion mechanism. As a consequence, these colorants readily diffuse into the nylon polymer structure causing a stain. There are, however, stain removal method such as that disclosed in U.S. Pat. No. 6,300,299 for mustard using peroxide and uv light and for betadine using household bleach solutions or bleach and bisulfite containing cleaning chemicals.
Ironically, recommended methods and cleaning agents for removing iodine and mustard stains can themselves damage dyes on acid dyed nylon fibers, therefore causing dye fading. Colorant pigments in solution dyed fibers are not effected by cleaning chemical products or benzoyl peroxide in acne care products. Unfortunately, many multicolored commercial carpet styles contain both acid dyed nylon fibers and solution dyed nylon fibers for color effects and styling. This tends to compound the problem when deciding which cleaning method and cleaner to use.
Accordingly, it is seen that a need has long remained for a process for protecting acid dyes from chemical agents and nylon fibers from neutrally charged colorants. It thus is the provision of such that this invention is primarily directed.
In a preferred form of the invention acid dyeable and cationic dyeable nylon fibrous products colored by either acid dyed (mill) processes, solution dyed (fiber) processes, or combinations thereof, are treated with a high level of sulfonated aromatic aldehyde condensation product (SAC) and then fixed by the wet heat method. By high level is meant at least 2% wt/wt (dry weight SAC/dry weight nylon fiber). So treated, the nylon fibers in dyed nylon are protected from staining by neutrally charged colorants and the dyes in the dyed nylon are protected from fading by chemical agents.
The reason for this phenomenon is not clear. High levels of methacrylate type stainblockers are totally ineffective in blocking neutrally charged colorants and chemical agents. Even the application of high levels of SAC are ineffective if fixed by the dry heat method. Apparently this new two step process closes the crystalline structure of the nylon fibers, a phenomenon previously observed in U.S. Pat. No. 5,350,426 which utilized a dry heat set method. In any event the process does render the dyed nylon fibers resistant to staining and chemical agents. Effective SAC anionic polymers are those described in Textile Chemist and Colorist, November 1989, Vol. 21, No. 11.